An echovirus is a type of RNA virus that belongs to the Enterovirus and the Picornaviridae virus family. The first isolation of echoviruses occurred from the feces of asymptomatic children early in the 1950s, just after cell culturing had been developed. The first part of the name echovirus is an acronym for "enteric cytopathic human orphan" virus. Echovirus is highly infectious, and its primary target is children. The echovirus is among the leading causes of acute febrile illness in infants and young children, and is the most common cause of aseptic meningitis. Infection of an infant with this virus following birth may cause severe systemic diseases, and is associated with high infant mortality rates. The echovirus can mimic symptoms caused by other common bacteria and viral infections, so echovirus infections are often treated with therapies aimed for other infections. This can lead to the creation antibiotics resistant bacteria.
An echovirus measures 24-30 nanometres (nm), and is similar to other virusses, since it has a naked protein capsid, which makes up 75% of the virus particle that encloses a dense central core of single-stranded RNA. This RNA has a length of approximately 7.5 kilobase (kb), contains an RNA replicase, viral-coded proteins, and a single polyprotein that is responsible for the formation of structural proteins and other proteins necessary for cellular replication. The structural proteins determine host range and play a very important role in delivering the RNA genome into the cytoplasm of new host cells.
Some viral replication of an echovirus occurs in the nasopharynx after infection and then spreads to regional lymph nodes. However, most viral particles are swallowed and they reach the lower gut tract, where the virus is presumed to bind to specific receptors. The virus then spreads to the lower intestinal tract, replicating but not causing any major cellular effects along the way. Next, the virus spreads to many secondary sites in the body such as the central nervous system, liver, spleen, bone marrow, heart and finally the lungs. Additional replication of the virus will occur, causing symptoms 4 to 6 days after infection. The most deadly part however is delayed when symptoms of a central nervous system disease start to appear. Enteroviruses are capable of infecting any cell in the body. These viruses are highly infectious. They can spread through the air to other hosts 1-3 weeks after infection and can spread through feces to other hosts eight weeks after infection.
The echovirus, and many of the diseases it causes, targets males in particular. Also, as noted before, infection within the first two weeks of birth can cause widespread systematic disease, resulting in death for many infants. As well, neo-natal children who are born prematurely fare even worse, as they will often die from infections anyways as their premature immune system cannot deal with the infections. Children who are born prematurely and die from echovirus infections usually die from overwhelming liver failure or myocarditis, rather than infection of the central nervous system. Older children and people of most other age groups have a better prognosis, but deaths still occasionally occur. In older patients, the primary infection source is the heart, and is usually fatal in 5% of cases.
Echovirus infections can occur in people of all age groups. However, as we get older, there is increased production of specific antibodies to the echovirus. Several studies performed during epidemics show that infants become infected at notably higher rates than older children and adults.
Causes of echovirus infections can be placed in several categories. Main causes of infection are from overcrowded conditions such as the poor districts of a city and poor hygiene. Echoviruses are transmitted person-to-person; the fecal-oral route is the predominant mode, although transmission sometimes occurs via respiration of oral secretions such as saliva. Indirect transmission occurs through numerous routes, including via contaminated water, food, and fomites (inanimate objects). Contaminated swimming and wading pools can also transmit the virus. Also, there are well-documented reports of transmission via the contaminated hands of hospital personnel.
Doctors can't do much once someone is infected. All any doctor can do is to administer IV therapy, which has some success in patients who have a compromised immune system and have persistent enterovirus infections, or they can administer a placebo. The effectiveness of anti-viral treatment is very uncertain; however, there are high hopes for the anti-viral drug pleconaril. This drug interferes with the binding of the echovirus particle to the cell membrane and the drug also hinders the uncoating of virions by attaching itself to the viral protein capsid. Phase III testing clinical trials are currently underway and the initial results look promising.